Antidepressants make for sad fish; drugs may affect feeding, swimming and mate-attracting.

In the fish world, baby is just another word for lunch. So it behooves aquatic larvae to be ever vigilant. But those that as embryos or hatchlings encounter water polluted with trace concentrations of antidepressants are much more likely to become food.

Tons of medicine ends up in the environment each year. Much has been excreted by patients, and leftover pills that have been flushed down the toilet may also contribute. Because water treatment plants weren't designed to remove pharmaceuticals, the water these plants release generally carries an array of drug residues.

In 2006, a pair of chemists reported that antidepressants downstream of water treatment plants were showing up in the brains offish.

Meghan McGee of St. Cloud State University in Minnesota set out to see if exposure to specific antidepressants would affect larval fathead minnows. Fish exposed as embryos or hatchlings to trace concentrations of the antidepressant venlafaxine, marketed as Effexor, didn't react as quickly as normal to stimuli signaling a possible predator. This laid-back reaction could prove to be a "death sentence," she observes.

McGee's is one of many studies probing behavioral impacts on aquatic wildlife from pharmaceutical pollution. Emerging data were reported November 16-20 at the North America annual meeting of the Society of Environmental Toxicology and Chemistry. Overall, the studies show that antidepressants can impair a fish's ability to eat, to avoid being eaten--and perhaps to attract a mate.

"I was surprised how often I was seeing these antidepressants," recalls Melissa Schultz of the College of Wooster in Ohio, one of the chemists who documented that antidepressants reach fish brains. "Pretty much any water sample in the vicinity of a wastewater treatment plant will test positive for some group of antidepressants."

The St. Cloud State results wouldn't be so bad if predators were also slowed by these similarly low concentrations. But such nanogram concentrations of fluoxetine, marketed as Prozac, didn't slow the speed at which hybrid striped bass scarf down fathead minnows, according to preliminary data reported by Joseph Bisesi Jr. of Clemson University in Pendleton, S.C., and his colleagues. Only at higher concentrations did some of the aggressive bass start to lose their voracious appetites.

Heiko Schoenfuss, leader of the St. Cloud study, also reported that fluoxetine functions like estrogen in the minnows and can diminish the facial bumps and coloration that females prize in mates.

Of course, all these experiments are quite artificial. Schultz says that a fish exposed to wastewater gets a dose of a lot of other things. "We'll have to look at how these might all interact," she says.

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